TM59 - Restricted Windows operation

Modified on Tue, 23 Jun at 12:42 PM

DesignBuilder V2025.1 has a new built-in function that will help you set the night restriction for CIBSE TM59.

This option is only available when using the 'Calculated Natural Ventilation' option in Model Options > Data > Natural Ventilation and Infiltration:

You can use the option to ‘Restrict venting factor by schedule’ available at Simulation screen > Calculation Options dialog >Output tab

This function will allow the %glazing area opens (Openings tab > Free Aperture) to be controlled by the Operation schedule.

The final openable area will be derived from the %glazing area opens * Schedule value.

There are two options to use this built-in function:

Option 1 - Set the % glazing area to 100% and adjust all schedules to correspond to the openable area.

Example:

A window that opens 50% daytime and 10% at night.

We can set the %glazing area opens = 100%, and create a custom operation schedule with 0.5 value during the daytime and 0.1 at night.

Schedule:Compact,
DayNightSchedule,
Fraction,
Through: 12/31,
For: AllDays,
Until: 08:00,
0.1,
Until: 23:00,
0.5,
Until: 24:00,
0.1;

In DesignBuilder interface:

Option 2 - Another approach is to input the glazing area opens as 50%, and adjust the schedule. When it can open 50%, set the schedule value = 1. When it can open only 10%, set the schedule value to 0.2 (0.2 * 50 = 10%)

Schedule:Compact,
DayNightSchedule,
Fraction,
Through: 12/31,
For: AllDays,
Until: 08:00,
0.2,
Until: 23:00,
1.0,
Until: 24:00,
0.2;

In DesignBuilder interface:

Note: when using this option, the openable area for all windows will be controlled by the schedule value. Therefore, it is important to set the correct operation schedule for all windows and avoid using the ‘follow occupancy’ option.